Swollen vulva on my chihuahua

Chocolate Pudding is about 2 years old and was spayed, about a year ago. I'm concerned because her vulva is really swollen and it looks like it really hurts. I just noticed it today, is this a common problem or should I rush her to the doctor? She's my best friend and I just want to make sure I do the right thing, as I can tell she has no clue what to do about it. Nor does she seem worried about it in the least... Thanks